High-order Harmonic Components Research Articles

Effect of positional errors on the accuracy of multi-probe roundness measurement methods

Multi-probe roundness measurement methods can be used to measure cross section roundness profiles and dynamic behaviour of large flexible rotors such as paper machine rolls. Other roundness measurement methods are not suitable for such measurements, since the rotors are too large to be measured on precision spindles and the center point of the measured profile can move in an unpredictable and unrepeatable way during the measurement. Multi-probe roundness measurement methods can, to a limited extent, separate the center point movement (commonly also called error motion) and the roundness profile of a cross section of a rotating workpiece.This study compares the effect of positional errors and center point movement on the accuracy of three different multi-probe roundness measurement methods. The research included quantification of the effects of probe noise, positional errors and center point movement on the accuracy of the roundness profiles produced by the different methods. A novel method for generating continuous random center point movement is presented. Signals of a rotating workpiece with center point motion were simulated, and following GUM handbook supplement 1 guidelines, the Monte Carlo method was used to obtain distributions for the harmonic components of the methods. Distributions for different errors and their effects on roundness parameters are presented separately for each roundness measurement method.The results of this research only show minor differences in lower order harmonic components between the methods. The results also show that diameter sampling is immune to horizontal positional errors although it is particularly sensitive to angular positional errors of the probes, which lead to more errors accumulating in the phases, not the amplitudes of the harmonic components. With higher order harmonic components, the obtained error distributions were observed to correspond well with theoretical error propagation rates for harmonic sensitivity.

Analysis of differences in vegetation phenology cycle of abandoned farmland, using harmonic analysis of time-series vegetation indices data: the case of Gwangyang City, South Korea

ABSTRACT Globally, countries have experienced substantial increases in farmland abandonment. Although vegetation phenology is a key factor for the classification of land use, understanding of the phenological change of abandoned farmland is lacking. Using harmonic analysis of NDVI and NDWI extracted from Landsat imagery, this study investigates the distinctive phenological characteristics of abandoned farmland, which contrasts with that of three other agricultural types (paddy, agricultural field, orchard) in the study site of Gwangyang City in Jeollanam Province, South Korea. The results suggest that abandoned farmland has higher overall greenness coverage and overall water content in vegetation than the other uses. In terms of both indices, abandoned farmlands changed with relatively less fluctuation than those of other uses, suggesting the existence of constant and unmanaged vegetation from ecological succession, which differs from crop fields that undergo cultivation procedures. The significant harmonic components differed among agricultural types and vegetation indices. In paddy, NDVI was explained with multiple, higher-order harmonic components, while in other types only first-order components met the 5% statistical significance level. With NDWI, land types were more clearly discernible, because of the different cultivation procedures involving water: wet-field method (paddy), dryland farming (orchard, agricultural field), and no cultivation (abandoned farmland). The analysis confirms that harmonic analysis could be useful in discerning abandoned farmland among areas of active agricultural use and shows that the statistical significance of harmonic terms can be employed as indicators of different agricultural types. The observed pattern of the geographic distribution of abandoned farmland has policy implications for the promotion of sustainable reuse of marginal farmland.

A Rotor Flux Observer of Permanent Magnet Synchronous Motors With Adaptive Flux Compensation

Due to the influence of current sampling and current reconstruction deviation, non-linearity of the inverters and parameter variation of the motors, DC offset component and high-order harmonic components exist in flux model, which makes the estimation of traditional rotor flux observer inaccurate and even divergent. In this paper, a rotor flux observer of permanent magnet synchronous motors (PMSM) with adaptive flux compensation is proposed. The DC offset component and the high-order harmonic components with the flux integrator observer can be eliminated by fed them back to the input of the flux integrator through PI regulator, so that the output of the flux integrator observer only contains the fundamental component, thus the rotor flux can be accurately estimated. Since the parameters of PI regulator are related with the estimated motor angular velocity, the control system has good robustness in a wide speed range. The flux observer is based on the voltage model in stationary coordinate system, so it is suitable for both surface and interior PMSMs. Moreover, the control method of the whole system has less computational complexity and fewer variables, it is easy to implement on a low-cost hardware platform. Finally, the experimental results verify that the flux observer has superior performance.

Analysis and design of modular open‐loop LED driver with multi‐channel output currents

In view of some applications for red green blue (RGB) light-emitting diodes (LEDs), a modular multi-channel constant-current LED driver is getting more important to obtain desirable colour and brightness. A multi-channel constant-current LED driver is proposed according to the constant-current characteristics of the passive LCL-T resonant network, which is composed of one high-frequency half-bridge inverter and as many passive LCL-T resonant rectifiers as the number of output channels. Only one passive resonant rectifier is added to increase a constant-current output channel, thus, it is easy to achieve multi-channel constant-current output as needed. In practical applications, the control can be simplified and the reliability can be improved in the open-loop mode. However, any change of input and output voltage would cause a certain fluctuation in the output current considering the high-order harmonic components in the open-loop mode. To this end, the precise solution of the actual output current is obtained in the paper. The quantitative parameter design has been completed according to the desirable current to meet the output constant-current accuracy within the given input and output. Finally, a 120-W prototype with three different constant-current outputs is built to verify the correctness of theoretical analysis.

Flux Observer Model for Sensorless Control of PM BLDC Motor With a Damper Cage

Sensorless control methods are commonly employed to derive the rotor position and speed information indirectly in permanent magnet (PM) brushless motor drives. Thereinto, the simple yet effective flux observer method is extensively applied in a wide range of applications. However, damper cage is sometimes employed in the rotor of certain PM brushless motor. Normally, high-order current harmonic components occur in such damper cage during operations. The introduction of these extra current contents can significantly hinder the performance of the conventional flux observer. By applying Park transformation, the fundamental harmonic components of stator phase currents, flux linkages, and voltages during steady-state operation, become constants under rotor synchronous reference frame, while the currents in the rotor damper cage are still alternating. In this paper, an improved flux observer method is proposed to filter the harmonic contents under the rotor synchronous reference frame for PM brushless motor with rotor damper cage. The validity and performance of the proposed flux observer are verified by both numerical analysis and experimental results.

Hybrid approach for immunisation of DFT‐based phasor estimation method against decaying DC components

In addition to high-order harmonic and noise components, the fault current may contain decaying DC components which highly affect the estimated fundamental frequency phasor. This study presents a new hybrid method which aims to calculate and remove the unwanted effect of decaying DC components on fundamental phasor estimation. The main novelty of the proposed method is that the proposed method is independent of the dynamic behaviour of the current transformer (CT). In other words, unlike previously published papers, this method analytically calculates the CT time constant. To such aim, utilising frequency modulation, fault current signal is shifted. Utilising simple but comprehensive formulations based on integration and Prony-complex theory, the magnitude and time constant of decaying DC components are calculated in one cycle. After that, utilising a modified discrete Fourier transform the fundamental phasor component is calculated. Several test signals and also practical fault signals are applied to the proposed method. The simulation results illustrate the proposed method simply but comprehensively remove the unwanted effects of the decaying DC components. Also, it has quick speed as well as a high-precision response in the estimation of fundamental phasor under different simulation scenarios.

On the Development of a Simulation Strategy to Model the Behavior of Graphene-Based Devices in Electromagnetic Simulators

This paper presents a new simulation strategy to be implemented in electromagnetic simulators in order to calculate the level of the induced high-order harmonic components in mono- and bi-layer graphene flakes when they are driven by an input electromagnetic field and to evaluate the frequency response of structures, including graphene. The technique is applied to the design and analysis of a single-stage high-order frequency multiplier capable of generating an output signal in the 220–330-GHz range from an input signal in the 26–40-GHz bands, whose topology is based on a structured graphene sheet enclosed in a waveguide resonant cavity that maximizes the incident electromagnetic field. A prototype was implemented to validate the method, obtaining a good agreement with the simulation results. Furthermore, the prototype was also used to experimentally characterize the performance of the multi-layer graphene sheets. In this case, the developed model is used to calculate the frequency response of the structure, but it is not able to predict the output power since the mathematical model describing the frequency conversion phenomena cannot be extrapolated to the multi-layer graphene. Several configurations were tested in order to determine the influence of the graphene sheet’s thickness and shape on the output power. Finally, a −33-dBm level output signal at 280 GHz was generated as the seventh-harmonic component of an input signal with a frequency of 40 GHz, showing that the presented prototype can be used as a signal generator in practical submillimeter-wave applications.

330-500 GHz Graphene-Based Single-Stage High-Order Subharmonic Mixer

In this work, a graphene-based single-stage high-order subharmonic mixer is presented. The device is able to up- and downconvert a signal in the 330-500 GHz frequency range, using a local oscillator signal with frequency located in the 26-40 GHz band. It exploits the strong nonlinear electromagnetic behavior exhibited by macroscopic graphene sheets when they are exposed to an incident electromagnetic wave to generate the output signal as a mixing product between the input signal and a high-order harmonic component of the local oscillator, which is internally generated without requiring additional circuitry. A prototype was implemented and its performance was experimentally characterized considering several different local oscillator multiplication orders. The maximum measured downconversion gain is around -50 dB, whereas the maximum output signal reached when working as upconverter is -43 dBm at 340 GHz and -63 dBm at 480 GHz. These values are good enough to be used in practical short-range applications. Furthermore, the measurement results are in good agreement with the theoretical predictions about graphene behavior.

Submillimeter Wave High Order Frequency Multiplier Based on Graphene

In this paper, a single stage millimeter/submillimeter wave frequency multiplier is presented. The desired frequency multiplication performance is obtained through the nonlinear excitation of high-order harmonic components in a graphene film, when it is illuminated with a low-frequency input signal. The graphene film is integrated into a microstrip structure on a polyimide substrate, which is subsequently embedded in a micromachined waveguide block. The design has been optimized to receive an input signal in the Ka frequency band, between 26.5 and 40 GHz, and to produce an output signal in the WR-3 frequency band, between 220 and 330 GHz. A complete prototype of the frequency multiplier module, including standard waveguide flanges for its interconnection, has been manufactured and experimentally characterized. The results in terms of output power in the WR-3 frequency band, for harmonic orders between 6 and 11, as well as for input power levels between 7 and 21 dBm, are presented.

On hydrodynamic characteristics of gap resonance between two fixed bodies in close proximity

The resonant water motion inside a narrow gap between two identical fixed boxes that are in side-by-side configuration is investigated using a two-dimensional (2D) numerical wave tank based on OpenFOAM®, an open source CFD package. Gap resonance is excited by regular waves with various wave heights, ranging from linear waves to strong nonlinear waves. This paper mainly focuses on the harmonic analyses of the free-surface elevation in the narrow gap and wave loads (including the horizontal wave forces, the vertical wave forces and the moments) on the bodies. It is found that the influences of the incident wave height on the higher-order harmonic components of different physical quantities are quite different. The effects of the incident wave height on the reflection, transmission and energy loss coefficients are also discussed. Finally, aiming at the quantitative estimation of the response time and the damping time of gap resonance, two different methods are proposed and verified for the first time on gap resonance.

Experimental study of wave loads on a small vehicle in close proximity to a large vessel

Operations involving the launch or recovery of a smaller vessel from a larger one are extremely dangerous in high sea states and, therefore, they are normally carried out in low to moderate sea states. However, this can be severely restrictive and in some situations, carrying out such operations in high sea states is unavoidable. Here we report on a detailed investigation of the interaction between two vessels of different size in order to characterise their hydrodynamic interaction under different conditions and to provide insight for operational purposes. Model experiments were conducted to investigate the hydrodynamic interaction between two vessels in close proximity in waves. Previous studies into this interaction have focused on two vessels with comparable size/displacement. This study focused on the interaction between vessels of very different sizes, a platform supply vessel and a lifeboat, at various separation distances between the two models and wave headings. It is found that the effect of the hydrodynamic interaction on the wave loads on the lifeboat model is substantial. The load responses show a strong non-linearity (high order harmonic components). In head waves, the effect of the hydrodynamic interaction on the wave loads is greater in the transverse modes (sway, roll and yaw) than in the longitudinal modes (surge, heave and pitch). The sheltering effects of the larger model on the lifeboat model were also evident from the experiments. The results of this investigation may be used to inform the planning of marine operations, such as the launch and recovery of a lifeboat or an Autonomous Underwater Vehicle (AUV) from a mothership and the transfer of equipment or personnel between vessels. The data will also provide a useful resource for validation of Computational Fluid Dynamics (CFD) codes and other numerical simulations, and can be used to better understand the limitations and potential widening of the operational weather windows and to ensure that operations are carried out safely.

Floquet-theoretical formulation and analysis of high-order harmonic generation in solids

By using the Floquet eigenstates, we derive a formula to calculate the high-order harmonic components of the electric current (HHC) in the setup where a monochromatic laser field is turned on at some time. On the basis of this formulation, we study the HHC spectrum of electrons on a one-dimensional chain with a staggered potential to study the effect of multiple sites in the unit cell such as the systems with charge density wave order. With the help of the solution for the Floquet eigenstates, we analytically show that two plateaus of different origins emerge in the HHC spectrum. The widths of these plateaus are both proportional to the field amplitude, but inversely proportional to the laser frequency and its square, respectively. We also show numerically that multistep plateaus appear when both the field amplitude and the staggered potential are strong.

Influence of magnetization pattern in three-phase permanent magnet synchronous machines

This paper investigates the influence of different magnetization patterns in the performance of three-phase permanent magnet synchronous motors (PMSMs). Three magnetization patterns widely used in surface-mounted PMSMs are radial magnetization, parallel magnetization and Halbach magnetization. In this paper, these magnetization patterns are applied to 9-slot/10-pole and 12-slot/10-pole surface-mounted PMSMs. The electromagnetic characteristics and performance of the motors such as air gap flux density distributions, phase back-emf, cogging torque, unbalance magnetic force and output torque are intensively evaluated in 2D finite element method. Important findings indicate that PMSMs with ideal Halbach magnetization exhibit almost zero cogging torque and sinusoidal phase back-emf waveform. Parallel magnetization and radial magnetization yield more trapezoidal phase back-emf waveform which results in higher torque ripples. One way to minimize the torque ripples is by reducing the higher-order harmonic components in the phase back-emf waveform which can be achieved with the best value of magnet pole arc. Additionally, a potential cost saving can be realized since the motor has smaller magnet volume as being demonstrated in the case of 9-slot/10-pole, three-phase surface-mounted PMSM in this paper.

Coherent X-ray source generation with off-resonance laser modulation.

The generation of ultrashort coherent radiation in the extreme-ultraviolet (EUV) and soft X-ray regimes is of great significance in a broad range of research. In this paper, a promising scheme for generating coherent harmonic radiation using off-resonance seed laser modulation is discussed. The off-resonance seed laser, whose wavelength differs from the resonant wavelength of the undulator, is first used to modulate the angular distribution of the electron beam (e beam) in the undulator (modulator). After passing through a dispersion section, strong coherent micro-bunching is introduced into the e beam, which contains high-order harmonic components of the seed laser. Theoretical analysis and simulations indicate that this method can be used for the generation of coherent EUV and soft X-ray radiation at sub-gigawatt power in a meter-scale undulator (radiator).

Superharmonic vibration and its reduction in SSD control by increase of voltage inversion time

The semi-active synchronized switch damping (SSD) approach has been widely used in vibration suppression owing to its many advantages compared with the active and passive approaches. The SSD method is realized by switching the voltage on the piezoelectric patch embedded in the structure, synchronically with the vibration of the mode to be controlled. Although good control performance can be obtained in the targeted mode, vibrations of high-order harmonic frequencies are usually excited due to the rectangular waveform of the switched actuator voltage because of infinitesimal inversion time, as observed in the previous experiments. This drawback of the SSD method has greatly hindered its application in practical engineering structures. In order to overcome this drawback, the authors propose a new method in this study to suppress the high-order harmonic components in the switched voltage by increasing the inversion time of the voltage. The theoretical expressions of the switched voltage and the dynamic response of the structure were formulated for the cases with finite voltage inversion time. The theoretical results show that increasing the inversion time may weaken the vibration control effect of the targeted mode, but it can significantly reduce the excitation force of the high-order harmonic components. When the inversion time is half of the period of the targeted mode, all the high-order harmonic components in the actuator voltage are completely erased and the control force of the targeted mode decreases by 21%. An experimental setup of a flexible beam was used to verify the theoretical results of the switched voltage and control performance under different inversion time.

An experimental decomposition of nonlinear forces on a surface-piercing column: Stokes-type expansions of the force harmonics

Wave loading on marine structures is the major external force to be considered in the design of such structures. The accurate prediction of the nonlinear high-order components of the wave loading has been an unresolved challenging problem. In this paper, the nonlinear harmonic components of hydrodynamic forces on a bottom-mounted vertical cylinder are investigated experimentally. A large number of experiments were conducted in the Danish Hydraulic Institute shallow water wave basin on the cylinder, both on a flat bed and a sloping bed, as part of a European collaborative research project. High-quality data sets for focused wave groups have been collected for a wide range of wave conditions. The high-order harmonic force components are separated by applying the ‘phase-inversion’ method to the measured force time histories for a crest focused wave group and the same wave group inverted. This separation method is found to work well even for locally violent nearly-breaking waves formed from bidirectional wave pairs. It is also found that the $n$th-harmonic force scales with the $n$th power of the envelope of both the linear undisturbed free-surface elevation and the linear force component in both time variation and amplitude. This allows estimation of the higher-order harmonic shapes and time histories from knowledge of the linear component alone. The experiments also show that the harmonic structure of the wave loading on the cylinder is virtually unaltered by the introduction of a sloping bed, depending only on the local wave properties at the cylinder. Furthermore, our new experimental results reveal that for certain wave cases the linear loading is actually less than 40 % of the total wave loading and the high-order harmonics contribute more than 60 % of the loading. The significance of this striking new result is that it reveals the importance of high-order nonlinear wave loading on offshore structures and means that such loading should be considered in their design.

Dynamic shear rheology of colloidal suspensions of surface-modified silica nanoparticles in PEG

The present work illustrates the effect of surface modification of silica nanoparticles (500 nm) with 3-(glycidoxypropyl)trimethoxy silane which was carried out at different reaction times. The suspensions prepared from modified and unmodified silica nanoparticles were evaluated for their shear rate-dependent viscosity and strain-frequency-dependent modulus. The linear viscoelastic moduli, viz., storage modulus and loss modulus, were compared with those of nonlinear moduli. The shear-thickened suspensions displayed strain thinning at low-frequency smaller strains and a strong strain overshoot at higher strains, characteristics of a continuous shear thickening fluids. The shear-thinned suspension, conversely, exhibited a strong elastic dominance at smaller strains, but at higher strains, its strain softened observed in the steady shear viscosity plot indicating characteristics of yielding material. Considering higher order harmonic components, the decomposed elastic and viscous stress revealed a pronounced elastic response up to 10% strain and a high viscous damping at larger strains. The current work is one of a kind in demonstrating the effect of silica surface functionalization on the linear and nonlinear viscoelasticity of suspensions showing a unique rheological fingerprint. The suspensions can thus be predicted through rheological studies for their applicability in energy absorbing and damping materials with respect to their mechanical properties.

Исследование магнитных систем высокоскоростных минитурбогенераторов с постоянными магнитами

The article presents the results from numerical calculation of the electromagnetic field for three different design versions of permanent magnets used in highsp eed mini turbine generators: with radially magnetized annular sectors, and with solid and hollow cylinders magnetized over the diameter. It has been found from a comparative investigation that permanent magnets in the form of solid and hollow cylinders magnetized over the diameter can be made with smaller diameter and active length as compared with their versions magnetized over the radius. Additional advantages of the design version in the form of a solid (hollow) cylinder magnetized over the diameter are that the i nduction distribution curve in the air gap contains almost no higherorder harmonic components, that the machine has higher synchronizing torque values, and that the probability of magnet failurefree opera tion at the working temperatures is close to unity.

Measurement of pre-bunched beam’s longitudinal form factor based on radiation from a tunable-gap undulator

The form factor, representing the statistical characteristics of a bunch's longitudinal distribution, is one of the most essential properties of a pre-bunched electron beam and is used for many types of frontier accelerator applications. We demonstrated the measurement of a pre-bunched beam's longitudinal form factor component based on coherent radiation from a widely tunable-gap undulator. The radiation energy from bunches with different longitudinal properties was measured as a function of undulator gap. The root-mean-square length of a 60 pC ultrashort quasi-Gaussian bunch generated by linac and chicane compression ranged from 75 fs to 240 fs, as obtained by fitting the radiation energy curve. Furthermore, the form factor component of the bunch train based on nonlinear longitudinal space charge oscillation was measured, and a higher-order harmonic component was observed with the proposed method than with the widely used coherent transition radiation method. The proposed method may satisfy the requirements of sub-fs bunch length measurement with proper undulator design.

Improved In-Line Vortex-Induced Vibrations Prediction for Combined In-Line and Cross-Flow Vortex-Induced Vibrations Responses

Slender marine structures are subjected to ocean currents, which can cause vortex-induced vibrations (VIV). Accumulated damage due to VIV can shorten the fatigue life of marine structures, so it needs to be considered in the design and operation phase. Semi-empirical VIV prediction tools are based on hydrodynamic coefficients. The hydrodynamic coefficients can either be calculated from experiments on flexible beams by using inverse analysis or theoretical methods, or obtained from forced motion experiments on a circular cylinder. Most of the forced motion experiments apply harmonic motions in either in-line (IL) or crossflow (CF) direction. Combined IL and CF forced motion experiments are also reported. However, measured motions from flexible pipe VIV tests contain higher order harmonic components, which have not yet been extensively studied. This paper presents results from conventional forced motion VIV experiments, but using measured motions taken from a flexible pipe undergoing VIV. The IL excitation coefficients were used by semi-empirical VIV prediction software vivana to perform combined IL and CF VIV calculation. The key IL results are compared with Norwegian Deepwater Programme (NDP) flexible pipe model test results. By using present IL excitation coefficients, the prediction of IL responses for combined IL and CF VIV responses is improved.